The invention relates to the field of liberating and removing gas that may be entrained in the form of small bubbles in drilling fluid. Basically this contemplates degassing drilling mud such as this term is employed in referring to drilling fluids used in oil well drilling operations.
Typically in well drilling operations substantial quantities of a specially formulated drilling mud or fluid are pumped down through the drill stem to be discharged through apertures located at the drill bit. This drilling mud serves not only to lubricate the drill bit and to remove the displaced rock, sand and other materials from adjacent the bit to a discharge point on the surface of the well site, but also to prevent the escape or blow out of natural gas which may be encountered in conjunction with the drilling operation. In connection with the flow of the drilling mud from the drill bit to the well site surface the mud frequently becomes contaminated with natural gas or air, appearing in the mud in the form of entrained minute bubbles of gas. Considering the cost of the specially formulated drilling mud it is economically desirable to recycle the special drilling mud back through the well instead of continuously supplying new drilling mud material. However, the presence of entrained gas bubbles in the drilling mud, decreases its density and substantially diminishes its efficiency in lubricating the drill bit and its effectiveness to prevent well blow-outs. Accordingly, it is desirable to degas the drilling mud to prepare it for recycling in connection with subsequent well drilling operations.
To perform this required degassing operation, special degassing concepts and systems have been suggested heretofore. The physical characteristics of the drilling mud, particularly its abrasiveness and its high viscosity, generally make liberation of entrained gas bubbles difficult. Frequently, prior art drilling mud degassing has involved centrifugal pumps or other rotary impellers employed to obtain the necessary agitation of the viscous drilling fluid. One drawback found in prior art proposals has been the tendency of the highly viscous drilling fluid to flow around the reciprocating agitator without experiencing the substantial mixing action needed. Such gas that may be removed from the mud immediately adjacent the agitator may not include the gas in the drilling mud that is adjacent the walls of the degassing apparatus.
One prior art degassing proposal for drilling fluids, is set forth in Burnham Sr. et al. U.S. Pat. No. 3,975,171 issued Aug. 17, 1976. Under the teachings of this patent, a cavitator is rapidly reciprocated within a conduit through which the drilling fluid is flowing. The cavitator is located within this flow of drilling fluid and its reciprocating action promotes coalescence of small entrained gas bubbles within the drilling fluid which may then rise more readily to the upper surface of the fluid for removal of this liberated gas.